System and method for carrying out a discontinuous rectification or reaction

ABSTRACT

The invention is an apparatus and process for batch rectification or reaction with batch distillation. The apparatus is a rectifying column alone or mounted on a batch reactor. The rectifying column having a collector for the downflowing column liquid arranged to collect liquid flowing down the column and a valve arrangement to direct the flow selectively away from the column or to the column at a time when downflowing product is being removed from the column. The column is operated at total reflux until the product reaches a required purity then the liquid flow from the collector is directed away from the column and the product recovered.

This invention relates on the one hand to a plant for carrying out batchrectification in a rectifying column or for carrying out a chemicalreaction in a batch reactor surmounted by a rectifying column, therectifying column being designed for operation under total reflux andcomprising at least one column section for material transfer, at leastone product vessel below the column section for collecting andtemporarily storing the liquid which has flowed downwards through thecolumn section and at least one other product vessel for collecting andtemporarily storing the head product.

The column section for material transfer may differ in design accordingto the nature of the rectifying column. Plate and packed columns andspecial constructions, such as wetted-wall and trickle columns, and alsorectifying columns with rotating internals (spray columns) and othertypes of construction may be used. The invention is not limited to aparticular type of column. However, a packed column with built-inpackings is preferred, as will be explained in the following.

In conventional batch distillation or rectification, the individualfractions are successively distilled off overhead in order ofvolatility. The individual fractions are preferably removed in atime-constant concentration as the reflux ratio gradually increases. Thedisadvantage here is that the reflux ratio has to be carefullycontrolled and that operating errors during production can seriouslyimpair the purity already achieved in the collected product. The lastbatch of product entering the product tank can affect the quality of thecontents so seriously that the entire contents of the tank have to beworked up again. This is particularly the case when very high productpurities have to be, or are intended to be, achieved.

To solve this problem, it is known that the batch rectification can becarried out under total reflux and that product vessels can be providedat the head of the column and, optionally, in the middle, too, for thepurpose of collecting the liquid accumulating at the particular point ofthe column and releasing it after a certain time. Accordingly, theseproduct vessels are designed for temporary storage of the liquidaccumulating at the particular point of the column.

A few years ago, this multivessel batch distillation was the subject ofan in-depth study. However, the experiments involved in that study wereonly conducted on a laboratory scale and pilot scale (Warter, Michael:“Batch-Rektifikation mit Mittelbehälter”, Fortschr.-Ber. VDI Reihe 3 No.686, VDI Verlag Düsseldorf, 2001).

The first advantage of this so-called “cyclic method of operation” isthat the best possible theoretical separation efficiency can be obtainedfor the plant used. This can be graphically demonstrated very easilywith the known McCabe-Thiele diagram for binary mixtures because, inthis case, the linear working curve coincides with the diagonal, so thatthe best separation efficiency is achieved. Accordingly, multivesselbatch distillation is particularly suitable for the production ofhigh-purity products. The advantage here is that there is no need forstrategies for the current change in the reflux ratio, as is normallythe case with conventional batch rectification.

The second advantage of the cyclic method of operation is that theproduction of specific product qualities can be carried out very safelywith multivessel batch distillation. In the cyclic method, no productleaves the system balance space to begin with because there is nofurther transport into the product tanks. Only when the productqualities satisfy the predetermined quality criteria is product pumpedinto the product tanks. In this way, the possibility of operator errorsduring production is greatly limited. This is particularly important inthe production of products expected to satisfy very stringent purityrequirements because, in the event of an operator error in conventionalbatch rectification, the last batch of product entering the product tankcan critically affect the quality of the high-purity product hithertocollected in the tank. This disadvantage is avoided by the describedcyclic procedure.

Other advantages of the cyclic method of operation lie in thesimultaneous production of several marketable products over all theproduct vessels, in a saving of time and in possible savings of energyby virtue of the heat-integrated system and, hence, in a reduction inthe production costs.

A special version of multivessel batch distillation is a column withonly one upper product vessel (head/distillate vessel) and with the baseof the column as another product vessel. In this case, only twoproducts, namely the head and bottom products, can of course besimultaneously produced under total reflux.

However, serious problems arise in the cyclic method of operation whereit is to be carried out an industrial production scale, as explained inthe following. In the known rectifying column 1 shown in FIG. 1, aconcentration profile is naturally developed. At least two componentsand usually several components are present in each of the individualcolumn sections. This means that, for example in the lower columnsection with the packings 7,8, one or more components of the secondproduct 3′ and third product 4′ must always be present. The same appliesto all other column sections. These components form the liquid holdup inthe column which is made up of the holdup on the packing elements andpackings. In addition, another type of holdup is important, above all incolumns with modern packings, namely the holdup in the collectors anddistributors not shown in FIG. 1. The holdup in the collectors inparticular is crucially important.

As already mentioned, the cyclic mode of operation with a multivesselstructure is distinguished by the fact that the individual vessels areemptied and the entire holdup of the product vessel is pumped into theproduction tanks. If this is carried out for all product vessels (thebase of a rectifying column being taken as a product vessel), the energysupply to the evaporator system is automatically interrupted duringemptying. In view of the greatly reduced volume of liquid at the base,the circulating stream in forced-circulation evaporators, for example infalling-film evaporators, or in natural circulation evaporators breaksup and can no longer be maintained. The hydrodynamic conditions in thecolumn are thus seriously disrupted. As a result of these events, thepressure profile in the column collapses and the hydrodynamicequilibrium between the ascending vapor phase and the downwardly flowingliquid phase can no longer be maintained. The outcome of this is thatthe entire holdup flows into the individual product vessels and impairsproduct quality. This is of particular relevance to high productpurities because, in this case, the high purity requirements in theindividual product vessels can no longer be satisfied. Accordingly,where the known process and the known plant are used, high-purityproducts cannot be produced by multivessel batch distillation on anindustrial production scale.

If multivessel batch distillation is carried out on a laboratory scale,this problem generally does not arise on termination of the process. Inthis case, the primary concern is not a high product yield, but ratherthe production of product patterns of predetermined high purity.Accordingly, the bottom vessel is only emptied to a relatively smallextent in order to establish the product pattern, the product remainingin the bottom vessel being present in a sufficient quantity so that thesupply of heat is maintained and the above-mentioned problem does notarise on termination of the process on an industrial production scale.The same applies to the production of product samples by partialemptying of the other product vessels.

Accordingly, the problem addressed by the invention was to make itpossible—in a plant of the type mentioned at the beginning—reliably toobtain high product purities and yields in the operation of the plant onan industrial production scale.

In a plant of the type mentioned at the beginning, the solution to theproblem stated above as provided by the invention is characterized inthat an arrangement is provided for selectively guiding the liquid intothe product vessel located below the column section or past that productvessel.

In this way, the plant can be operated as follows: first, the rectifyingcolumn is operated under total reflux, the arrangement mentioned guidingthe liquid into the product vessel where the liquid is collected andtemporarily stored and, finally, is returned to the column. If a steadyoperating state of the plant is reached, the product quality in theproduct vessels meeting predetermined requirements, the product vesselscan be completely emptied without the holdup flowing downwards into theproduct vessels and impairing product quality because the arrangementmentioned is now reversed and guides the liquid flowing back past theproduct vessels.

In one particular embodiment, the column section containing the holdupcomprises at least one built-in packing and/or at least one built-inplate. In other words, a modern packed column and optionally a platecolumn are preferred.

The above-mentioned arrangement for selectively guiding the liquid candiffer in its design, depending in particular on the nature of theproduct vessel. If the product vessel below the column section is abottom vessel or a batch reactor, a collector is arranged between thelowermost column section, for example the lowermost packing of therectifying column, and the bottom vessel or the batch reactor and isconnected at its outlet to an auxiliary vessel and to the bottom vesselor to the batch reactor and the arrangement for selectively guiding theliquid comprises a first valve assembly. If the bottom vessel or thebatch reactor is to be emptied, this first valve assembly is actuated insuch a way that the holdup from the lowermost material transfer zone nolonger flows into the bottom vessel or into the batch reactor, but intothe auxiliary vessel and, hence, does not impair the high quality, moreparticularly the high purity, of the bottom product.

Basically, the downwardly flowing liquid can flow completely through theauxiliary vessel mentioned and from there into the bottom of the column,even when the column is operated under total reflux. In a preferredembodiment, however, the downwardly flowing liquid flows directly fromthe lowermost material transfer zone into the bottom vessel during thefirst phase of the process, a valve being provided at the outlet of thecollector located below the lowermost packing. To terminate the process,this valve is closed and another valve is opened to guide the liquidthrough a bypass into the auxiliary vessel. The same applies to a batchreactor surmounted by a rectifying column. Accordingly, it is expresslyproposed that the collector be connected via the first valve assembly onthe one hand to the auxiliary vessel and, on the other hand, to thebottom vessel or to the batch reactor. The first valve assembly mayconsist of an arrangement of several valves or of a single multiwayvalve.

As already mentioned, the plant according to the invention may be usednot only for physically separating mixtures, but also for carrying outchemical reactions, more particularly as a batch reactor surmounted by arectifying column. In this case, the bottom vessel corresponds to abatch tank reactor, for example a stirred tank reactor. A known plantcomprising a stirred tank reactor surmounted by a rectifying column isdescribed, for example, in EP 0 464 045 B1 (Henkel KGaA). In this case,however, the rectifying column is not designed for multivessel batchdistillation.

In order to produce a high-quality product accumulating in the middlepart of the column in accordance with the invention, it is proposed forthe plant according to the invention that the liquid flowing downwardsin the middle column section can be guided by a second valve assemblyinto a second product vessel, of which the outlet is connected to thelower column section, or into a bypass pipe leading around the secondproduct vessel. In contrast to the bottom vessel, the additional vesselprovided in this embodiment does not act as a collecting vessel for theholdup, but instead as a product vessel which is connected via suitablevalves to the column, i.e. on the one hand to the outlet of thecollector and, on the other hand, to the inlet of the underlyingdistributor. Of key importance here is the bypass pipe around the secondproduct vessel through which the holdup flows on termination of theprocess in order not to contaminate the holdup which has alreadycollected in the second product vessel.

Similarly, several product vessels of this type can be arranged alongthe column, but at different levels, i.e. below different central columnsections, the contents of the product vessels being identicallyprotected against the holdup flowing down on completion of the process.

So far as the production of the head product in the plant according tothe invention is concerned, it is further proposed that the productvessel for the head product, i.e. the distillate vessel, be connected tothe head of the column via a feed pipe, more especially with acondenser, and a reflux pipe.

Finally, the present invention also relates to a process for carryingout a rectification and/or a reaction in a plant of the type accordingto the invention.

In the process according to the invention, the problem stated above issolved by first carrying out the process under total reflux and guidingthe liquid for temporary storage into the product vessels and then, i.e.when the predetermined or desired specification, more particularly therequired purity, is reached, past the product vessels and emptying theproduct vessels.

Further advantages and several embodiments of the invention aredescribed in detail in the following with reference to the accompanyingdrawings, wherein:

FIG. 1 schematically illustrates a known multivessel batch distillationplant.

FIG. 2 is a perspective view of the middle part of a modern packedcolumn with a known packing (Sulzer packing).

FIG. 3 schematically illustrates a first embodiment of a multivesselbatch distillation plant according to the invention.

FIG. 3 a shows the lower part of the plant illustrated in FIG. 3 inanother variant according to the invention.

FIG. 4 schematically illustrates another embodiment of a plant accordingto the invention comprising a reactor surmounted by a rectifying column.

In all the drawings, the same reference numerals have the same meaningand, accordingly, may be explained only once.

One example of a known multivessel batch distillation plant isschematically illustrated in FIG. 1. Several product vessels 2, 3 arearranged along a standard batch rectifying column 1. The bottom of thecolumn is regarded as a product vessel 4 for the bottom product. Theliquid flowing down through the packings 5, 6, 7, 8 in the column 1 isremoved from the column and guided into a corresponding product vessel2, 3, 4. The products themselves are denoted by the reference numerals2′ for the head product, 3′ for the product temporarily stored in themiddle vessel 3 and 4′ for the bottom product. Several product vesselsmay also be arranged in the middle part of the column. After apredetermined volume of liquid has collected in the vessels 2, 3, aliquid stream is then removed from the vessels 2, 3 and returned to thecolumn 1 through the pipes 9 (with valve 10) and 11.

The column is thus operated under total reflux because no product streamis removed from the individual product vessels 2, 3, 4 and guided into aproduct tank. After a transition period, steady states are spontaneouslyestablished in all the product vessels 2, 3, 4. This means that thequality of the product in the individual product vessels is notsubjected to any more changes as a function of time and remainssubstantially constant. For this reason, this type of rectification isalso known as “cyclic rectification” to distinguish it from theconventional batch rectification procedure.

If the quality achieved satisfies the purity requirements for theindividual products, the second phase of the process is initiated, i.e.the valves 12, 13, 14 are opened and the products 2′, 3′, 4′ are removedfrom the individual product vessels 2, 3, 4 and guided into the producttanks 15, 16, 17.

If the product quality in the individual product vessels 2, 3, 4 doesnot correspond to the required product quality, more particularly therequired purity, the product volumes in the product vessels 2, 3, 4 areslightly changed by suitable changes to the process parameters, a newsteady state is allowed to develop and a decision is then made as tofurther procedure.

A condenser 18 known per se at the head of the column 1 and the bottomheater 19 known per se—for example in the form of a forced-circulationevaporator or a natural circulation evaporator—are also shown in FIG. 1.

For a better understanding of the significance of the volume of liquidstored in the collectors of a rectifying column, which leads to seriousproblems on termination of the known multivessel batch distillationprocess, FIG. 2 shows part of a conventional rectifying column. Thereflux from the condenser 18 is fed through the pipe 9 to a distributor20 and, from there, trickles uniformly downwards through the packing 21.The volumes of liquid issuing from the underneath of the packing 21 arecollected by obliquely positioned metal “lamellae”, i.e. by thecollector 22, and are fed through an annular passage 23 to anotherdistributor 24 which distributes the liquid uniformly over the top ofthe underlying packing 25. The lamellar collector 22 may be, forexample, a collector of the SLR type from Sulzer. Another pipe 26 whichopens into the annular passage 23 is provided in the middle part of thecolumn for introducing the liquid feed.

A plant according to the invention is schematized in FIG. 3 which showsa rectifying column 1 for separating a liquid mixture.

Besides the elements known per se, which were explained in thedescription of the plant shown in FIG. 1, the new features and elementsaccording to the invention will now be discussed in detail. Instead of asingle product vessel 3, several product vessels 3 may of course bearranged along the column in the middle part thereof. According to theinvention, certain arrangements are provided to prevent the contents ofthe product vessels 3, 4 from being mixed with the volumes of liquid onthe packings 5, 6, 7, 8, in the collectors 22, 30 and the distributors20, 24.

On the one hand, an auxiliary pipe 27 is installed parallel to theproduct pipe 11 in the region of the product vessel 3 and is designed tobe shut off by a valve 28. The product vessel 3 can be safeguardedagainst the liquid flowing down in the column 1 by another valve 29. Inaddition, an auxiliary valve 37 is arranged between the outlet of theproduct vessel 3 and the distributor 24. In the steady state establishedin the plant when the specified product quality is reached in theproduct vessel 3, the valves 29 and 37 are closed and the valve 28 isopened, so that the liquid flows directly from the collector 22 to thedistributor 24 and not into the product vessel 3. After the valve 13 hasbeen opened, the product vessel 3 is emptied into the product tank 16.

On the other hand, a different type of arrangement is shown in thelowermost region of the column and prevents the bottom product frommixing with the holdup on the overlying packings 7, 8 and in thedistributor 24 and the column internals situated further above. Theproposed diversion of the liquid stream in the middle part of the columnas a reflux stream from the column directly back into the column withoutthe detour via the product vessel cannot of course be accomplished herebecause, in this case, the liquid stream would pass into the bottom ofthe column where it would contaminate the bottom product 4′. Instead, anadditional collector 30 is installed below the lowermost packing 8. Thecollector 30 collects the entire liquid stream which would otherwisepass directly into the bottom vessel 4.

Until the steady state is established in all the product vessels, theentire liquid stream, which leaves the last packing section 8 and iscollected by the collector 30, is guided through the pipe 31 and theopened valve 32 into the bottom vessel 4. After the steady state hasbeen established in all the product vessels and shortly before all theproducts vessels and also the bottom vessel 4 are emptied, the liquidflowing from the outlet of the collector 30 is guided through the pipe31 and an opened valve 33 into an auxiliary vessel 34 which collects theholdup flowing downwards through the column. The valve 32 meanwhile isof course closed to prevent contamination of the bottom product 4′ bythe holdup. When the process is next carried out, the liquid mixturecollected in the auxiliary vessel 34 can again be mixed with the newfeed and worked up again. An advantage here is that no product losseshave to be accepted, so that particularly economical operation isguaranteed.

Alternatively, but not preferably, the auxiliary vessel 34 may also beinstalled in such a way (FIG. 3 a) that the entire volume of liquidreleased from the collector 30 always flows first into the auxiliaryvessel 34. After the steady operating state has been established, theauxiliary vessel 34 is first emptied into the bottom vessel 4 and thevalve 36 is then closed. The bottom vessel 4 is then emptied into theproduct tank 17 by opening of the valve 14 and closing of the valve 38,as in the preferred variant shown in FIG. 3.

In addition, an auxiliary pipe 39 with a valve 40 at the head of thecolumn (FIG. 3) is advantageous. In the steady operating state of theplant, the auxiliary pipe 39 is brought into operation by opening of thevalve 40 and closing of the valves 41, 42, so that the contents of theproduct vessel 2 are protected against any disturbances that couldcontaminate its composition.

The invention also encompasses the special case of multivessel batchdistillation where a column is provided with only one distillate vessel2 and a bottom product vessel 4 as the product vessel, but no so-calledmiddle vessel(s). Such arrangements are typified in particular by batchreactors known per se surmounted by a column as schematized, forexample, in FIG. 4 in an embodiment of the invention. Here, the productvessel 4 for the bottom product is in the form of a stirred tank reactor35. The other product vessel in FIG. 4 is the distillate vessel 2. Byvirtue of the advantages mentioned, the plant illustrated in FIG. 4 isoperated under total reflux. The attached rectifying column is also usedto remove the excess educt after the reaction. One example of such areaction is the production of an ester from an organic acid and analcohol as described, for example, in the above-cited EP 0 464 045 B1.In many cases, the useful component is a product of relatively lowvolatility from which the low-boiling constituents are to be removed.

In order to protect the contents of the reactor, which in many casescontains the useful component, from the holdup of the column 1 aftertermination of the reaction, an arrangement corresponding to FIG. 3 isprovided in the bottom region. After the low-boiling constituentscollected in the product vessel 2 have been removed, the valve 32 isclosed and the valve 33 opened, so that the holdup is guided from thecolumn 1 through the collector 30 and the pipe 31 not into the stirredtank reactor 35, but instead through the valve 33 into the auxiliaryvessel 34.

The plant shown in FIG. 4 is particularly suitable for high-puritybottom products which would suffer losses of quality by mixing with theliquid stream flowing down from the column 1. This leads to the furtheradvantage that the need for a distillation step to remove thelow-boiling constituents emanating from the holdup from the bottomproduct is eliminated.

The procedure in the head region of the plant shown in FIG. 4 during thereaction is explained in detail in the following with reference to thegeneral reaction:A+B

C+DThis reaction may be, for example, an esterification reaction whereA=alcohol, B=acid, C=ester and D=water. If—in the interests ofsimplicity—it is assumed that A, B, C and D are completely miscible, ahomogeneous mixture is present. The column is used for continuouslyremoving water (component D) from the reaction mixture with minimallosses of components A, B and C. The reaction equilibrium in the reactoris thus very favorably influenced. In order to minimize investmentcosts, the height of the column is kept to a minimum in practice. Sincethe greatest separation efficiency is achieved with total reflux, thefollowing procedure is adopted (FIG. 4), the valves 41, 42, 43 beingopen and the valve 40 closed.

Alternatively, the reaction may be the following:A+B

Cwhere a low-boiling product C is to be removed. The objective here is toobtain a “pure” product C in the distillate vessel 2. To this end, thevalves 41, 42, 43 are first opened and the valve 40 is closed. Whensubstantially the entire quantity of product C has collected in theproduct vessel 2 and unwanted secondary products of the reaction aregradually distilled off and threaten also to enter the product vessel 2,the auxiliary pipe 39 is brought into operation by opening of the valve40 and the valves 41, 42 are closed. The valve 43 of course remainsopen. In this way, the contents of the product vessel 2 are protectedagainst secondary products removed by distillation and against theexcess of component A or B.

An alternative to the auxiliary pipe 39 would be switching over in knownmanner to another parallel vessel 44 by means of another auxiliary pipe45. The other vessel 44 and the other auxiliary pipe 45 with the valvesare shown in chain lines in FIG. 4.

After termination of the reaction A+B

C+D, the water of reaction D which has collected in the vessel 2 isremoved—if it has not already been removed from the vessel 2 during thereaction—and the excess of component A or B is distilled off from thereaction mixture in order to obtain the high-purity useful product C.The excess of the educt component A or B is collected in the productvessel 2 which acts as a distillate receiver. It is desirable to achievea high concentration (purity) of the contents of the product vessel 2because this component is generally returned to the reactor and re-usedfor the next batch. A high concentration enables a high volume/timeyield to be achieved in the reactor with the next batch.

During removal of the excess of component A or B by distillation aftertermination of the reaction, the valves 41, 42, 43 are opened and thevalve 40 is closed.

After the desired composition has been reached in the product vessel 2,the following actions are taken in the order listed:

-   1. The valves 41, 42 are closed and the valve 40 in the auxiliary    pipe 39 is opened, the valve 43 of course remaining closed.-   2. The valve 33 is then opened and the valve 32 closed in order to    protect the useful product.-   3. The contents of the batch reactor 35, i.e. the useful product C,    are pumped into a product tank (not shown in FIG. 4).-   4. The contents of the auxiliary vessel 34 are pumped back to the    batch reactor 35.-   5. The contents of the product vessel 2 are also pumped back to the    batch reactor 35.-   6. The next batch is started with the measured introduction of    starting components A and B.

To sum up: the plant shown in FIG. 4 consists of a reactor 35 and acolumn 1. The first phase of the process comprises a reaction coupledwith a distillation, for example an esterification with removal of waterby distillation. The second phase of the process comprises only adistillation, for example removal of the excess of educts bydistillation. Accordingly, in the second phase, the plant behaves in thesame way as in conventional batch distillation. The difference here liesin the unusually large bottom vessel which is formed by the reactor. Inconventional batch distillation, however, the bottom vessel is not areactor.

EXAMPLE

An example of the process according to the invention was carried out inthe plant shown in FIG. 3. Two Sulzer BX packings each with a height of1 m were arranged in the 70 mm diameter column. Each of these packingscorresponded to 5 to 6 theoretical plates. The column was operated witha head pressure of 10 to 20 mbar, the pressure loss over the columnbeing 4 to 8 mbar. The bottom temperature was 130 to 140° C. Aconventional electromagnetic reflux divider (Normag) was used instead ofa collector.

2.9 kg of a test mixture of fatty alcohols with the followingcomposition were used: C6: 24.8% C8: 26.0% C10: 49.2%

A steady state was reached after 2.5 hours. In other words, thecompositions of the three products, i.e. the head product, the middleproduct and the bottom product, as measured with a gas chromatograph,remained constant.

Before emptying, the product vessels were protected in accordance withthe invention against the downwardly flowing holdup. The experimentallyobtained product compositions were as follows: C6: 98.8% C8: 98.1% C10:99.5%,the three products being analyzed by gas chromatograph.

These high product purities, which were obtained on only 5 to 6theoretical plates, are attributable to the mode of operation with totalreflux, which guarantees the highest possible system separationefficiency, and to the arrangement according to the invention forprotecting the products against the downwardly flowing holdup.

LIST OF REFERENCE NUMERALS

-   1 batch rectifying column-   2 product vessel for 1st product-   2′ head product-   3 product vessel for 2nd product-   3′ 2nd product-   4 product vessel for bottom product (3rd product), bottom vessel-   4′ bottom product-   5 packing (column section)-   6 packing (column section)-   7 packing (column section)-   8 packing (column section)-   9 pipe for distillate (condensate)-   10 valve-   11 pipe-   12 valve-   13 valve-   14 valve-   15 product tank for 1 st product-   16 product tank for 2nd product-   17 product tank for 3rd product (bottom product)-   18 condenser-   19 bottom heater-   20 distributor-   21 packing-   22 collector-   23 annular passage-   24 distributor-   25 packing-   26 feed pipe-   27 auxiliary pipe-   28 valve-   29 valve-   30 collector-   32′ pipe-   32 valve-   33 valve-   34 auxiliary container-   35 stirred tank reactor, batch reactor-   36 valve-   27 auxiliary valve-   38 valve-   39 auxiliary pipe-   40 valve-   41 valve-   42 valve-   43 valve-   44 additional container-   45 other auxiliary pipe

1-7. (canceled)
 8. An apparatus for carrying out batch rectification ina rectifying column or for carrying out a chemical reaction andrectification in a batch reactor surmounted by a rectifying column, therectifying column adapted for operation under total reflux, comprisingat least one rectifying column section for material transfer; at leastone column underflow product vessel for collecting and temporarilystoring a liquid which flows downward through the rectifying columnsection; an overhead product vessel for collecting and temporarilystoring an overhead product; wherein, an arrangement is provided forselectively guiding liquid, flowing down the rectifying column section,into the underflow product vessel or away from the underflow productvessel.
 9. The apparatus of claim 8, wherein, the column sectioncomprises at least one packing section or at least one rectifying plate.10. The apparatus of claim 8, wherein, the underflow product vesselcomprises a bottom vessel or a batch reactor; a collector is arrangedbetween a lowermost column section and the bottom vessel or the batchreactor to collect liquid which flows down the column, the collector isconnected at its outlet to an auxiliary vessel the outlet of theauxiliary vessel is connected to the bottom vessel or to the batchreactor via a valve which selectively controls the liquid flow to thebottom vessel or the batch reactor.
 11. The apparatus of claim 8,wherein the underflow product vessel comprises a bottom vessel or abatch reactor; a collector is arranged between a lowermost columnsection and the bottom vessel or the batch reactor to collect liquidwhich flows down the column, the collector is connected at its outlet toan auxiliary vessel via a first valve and to the bottom vessel or batchreactor via a second valve.
 12. The apparatus as claimed in claim 9,wherein a middle column collector is arranged to collect liquid whichflows downward in a middle column section; a second valve assemblyarranged to selectively guide the collected liquid into a second productvessel having an outlet which is connected to a lower column section, orto a bypass pipe arranged to bypass the liquid around the second productvessel.
 13. The apparatus as claimed in claim 8, wherein the overheadproduct vessel is connected to a head of the column via a feed pipe, acondenser, and a reflux pipe.
 14. A process for carrying out arectification or a reaction with rectification in the apparatus of claim8, wherein, the process is initially carried out under total reflux witha liquid flowing down a column section guided for temporary storage intoproduct vessels and when the composition of liquid product in theproduct vessels achieves a required purity, the liquid flowing down thecolumn section is guided away from the product vessels and at least aportion of the liquid product is removed from the product vessels. 15.The apparatus of claim 9, wherein, the underflow product vesselcomprises a bottom vessel or a batch reactor; a collector is arrangedbetween a lowermost column section and the bottom vessel or the batchreactor to collect liquid which flows down the column, the collector isconnected at its outlet to an auxiliary vessel the outlet of theauxiliary vessel is connected to the bottom vessel or to the batchreactor via a valve which selectively controls the liquid flow to thebottom vessel or the batch reactor.
 16. The apparatus of claim 9,wherein the underflow product vessel comprises a bottom vessel or abatch reactor; a collector is arranged between a lowermost columnsection and the bottom vessel or the batch reactor to collect liquidwhich flows down the column, the collector is connected at its outlet toan auxiliary vessel via a first valve and to the bottom vessel or batchreactor via a second valve.
 17. The apparatus of claim 9, wherein amiddle column collector is arranged to collect liquid which flowsdownward in a middle column section; a second valve assembly arranged toselectively guide the collected liquid into a second product vesselhaving an outlet which is connected to a lower column section, or to abypass pipe arranged to bypass the liquid around the second productvessel.
 18. The apparatus of claim 9, wherein the overhead productvessel is connected to a head of the column via a feed pipe, acondenser, and a reflux pipe.
 19. The apparatus of claim 10, wherein amiddle column collector is arranged to collect liquid which flowsdownward in a middle column section; a second valve assembly arranged toselectively guide the collected liquid into a second product vesselhaving an outlet which is connected to a lower column section, or to abypass pipe arranged to bypass the liquid around the second productvessel.
 20. The apparatus of claim 11, wherein a middle column collectoris arranged to collect liquid which flows downward in a middle columnsection; a second valve assembly arranged to selectively guide thecollected liquid into a second product vessel having an outlet which isconnected to a lower column section, or to a bypass pipe arranged tobypass the liquid around the second product vessel.
 21. The apparatus ofclaim 11, wherein the overhead product vessel is connected to a head ofthe column via a feed pipe, a condenser, and a reflux pipe.
 22. Theapparatus of claim 12, wherein the overhead product vessel is connectedto a head of the column via a feed pipe, a condenser, and a reflux pipe.